Scientific Forecaster Discussion
fxus66 klox 152353
Area forecast discussion
National Weather Service Los Angeles/Oxnard California
353 PM PST Sat Dec 15 2018
Increasing clouds are expected overnight and Sunday, as a storm
system approaches the coast. A weak cold front will bring rainy
conditions starting Sunday night on the central coast, spreading
south of Point Conception Monday morning. Rain is expected to
taper off late Monday afternoon. High pressure building in behind
the front will push temperatures above normal by Wednesday.
Short term (tdy-tue)...15/142 PM.
Patchy fog continues to linger in the interior valleys of northern
San Luis Obispo County, especially in and around Paso Robles.
Though the fog is beginning to diminish somewhat it has kept
temperatures chilly through the morning. Temperatures should warm
quite a bit once the fog thins but the forecast maximums were
tweaked downward a few degrees. There just will not be enough
daylight left to get good warming in the region. Patchy fog was
put into the forecast for tonight as it will likely reform though
to what extent is in question.
The remainder of the service area is experiencing good warming
today and some areas have had the Max temperature forecast bumped
up. The interior valleys and the Santa Monica Mountains of Los
Angeles County have multiple locations with double digit 24-hour
temperature increases. Depending upon how quickly the clouds move
in and thicken this could notably warm the overnight temperatures
and tomorrow afternoon temperatures as well.
Sunday will begin dry and relatively warmer as the cloud cover
continues to increase and lower. The low pressure centered off the
Aleutian Islands continues to deepen and this should strengthen
the cold front even down on the southern end as it moves toward
Southern California. This will strengthen the prefrontal southwest
winds as well as the cold punch of the northerly flow behind the
Light rain may begin in far northwestern San Luis Obispo County by
late Sunday then an increasing chance of rain will develop
overnight as far south as Point Conception. Locations from Santa
Barbara and northward will likely receive rain from a quarter inch
in the south to an inch or more to the north and in the higher
mountains. Rain across Ventura and Los Angeles counties is less
certain and what falls will be a tenth of an inch or less in most
locations and possibly up to a quarter inch in the mountains.
These rates are below those that would likely produce debris flow
problems. As always, though, precautions should be considered when
rain is forecast.
Minimal amounts of snow will fall above 6000 feet and likely near
7000 feet during this event.
Some lingering precipitation will continue across Ventura and Los
Angeles counties late on Monday and into early Tuesday.
Temperatures will be chilly on Tuesday.
Long term (wed-sat)...15/150 PM.
A moderate high pressure ridge builds in by Wednesday and Ushers
in dry and notably warming temperatures as weak offshore flow
develops. Temperatures will climb to above normal levels on
Wednesday and will warm further on Thursday with some locations
reaching 80 degrees or more. Temperatures will remain above normal
on Friday but will be cooler and by Saturday most locations will
be near normal. All locations will remain dry through the period.
At 2335z...there was a surface-based inversion at klax. The top
of the inversion was around 1800 ft with a temp of 17 deg c.
Generally hi confidence in the 00z tafs, except moderate
confidence for kprb, ksbp and ksmx due to LIFR cigs/vsbys expected
at times later tonight into early Sun morning then increasing to
IFR/MVFR conditions aft about 16z sun.
Otherwise, VFR conditions can be expected at the airfields through
Klax...hi confidence in the 00z taf with VFR conditions expected
thru Sun afternoon.
Kbur...hi confidence in the 00z taf with VFR conditions expected
thru Sun afternoon.
Moderate to high confidence in the current forecast. A moderately
large northwest swell across the coastal waters will persist
through tonight, then diminish some Sunday. Hazardous seas will
persist for periods of time across outer and northern coastal
waters through tonight.
Between Sunday night and Tuesday, a very large west-northwest swell is
expected to build into the coastal waters and affect west to
northwest facing harbors, including Morro Bay where dangerous
conditions are likely to occur at The Harbor entrance. Ventura
Harbor could also be affected on Monday through at least Tuesday
as some of the energy from the swell filters into the Southern
California bight. Moderate-to-high seas will then persist through
Otherwise, winds should remain below Small Craft Advisory (sca)
levels through Thursday except for a 50%-60% chance of Small Craft Advisory level
gusts at times for the southern two outer waters zones (pzz673 and
pzz676) Tuesday and Tuesday night.
High surf conditions will continue across the central coast
this weekend. From Sunday night through Tuesday, a very large
long period west-northwest swell (290 degrees) will impact
the central coast, likely bringing very large and potentially
damaging surf during that time. As a result, high surf warnings
and have been posted for the central coast due to the high
confidence in the event. Surf heights of 18 to 25 feet are
expected across the central coast, with local sets up to 30 feet
A coastal flood advisory has also been issued to coincide with
the timing of the high surf advisory. Water could spill into
normally dry beaches, beach parking lots and Harbor walkways.
Potential impacts include beach erosion, very strong rip currents,
possible damage to piers and coastal structures, as well as large
breaking waves into Morro Bay Harbor which could capsize small
Due to the long period nature of this swell energy (19 to 20
seconds), some of this large swell energy is expect to wrap
around into areas south of Point Conception impacting west-
facing beaches of la, Ventura, and southern sba counties.
High surf advisories have been issued for this area where west-
facing beaches will see 8 to 12 foot breakers, especially for the
Ventura County coast. Local sets to 15 feet are possible across
Ventura Harbor as well, with a 20 percent chance of needing to be
upgraded to high surf warning thresholds. Surf of 5 to 8 feet is
expected for the south Santa Barbara County coast, highest around
California...high surf advisory in effect until 9 PM PST Sunday for zones
34-35. (See laxcfwlox).
High surf warning in effect from 9 PM Sunday to 9 am PST
Tuesday for zones 34-35. (See laxcfwlox).
Coastal flood advisory in effect from 9 PM Sunday to 9 am PST
Tuesday for zones 34-35. (See laxcfwlox).
High surf advisory in effect from 4 am Monday to 10 PM PST
Tuesday for zones 39>41-87. (See laxcfwlox).
Pz...Small Craft Advisory for hazardous seas in effect until 3 am
PST Sunday for zones 645-670-673. (See laxmwwlox).
Hazard potential outlook (tue-sat).
There will be very high surf and dangerous rip currents through